Over the past several years, demand has increased for the efficient removal of contaminants from water supplies. Because of their relatively small size, many light density contaminants (e.g., microorganisms) have failed to be removed by conventional processing methods including fluid separation.
Fluid separation may include any process that captures and removes materials from a liquid stream, typically resulting in a clarified liquid having reduced contaminants and a denser stream containing removed contaminants. Further treating the denser stream in a thickening process may remove additional liquid to leave a thick, pump-able slurry mixture containing nine to approximately twelve percent solids by weight. Under certain conditions, a de-watering process may remove more water from the slurry mixture. The de-watering process may create a stackable but still moist mixture of approximately twelve to thirty percent solids by weight. In an extreme de-watering process, the resulting mixture may comprise up to forty percent solids by weight. In treating a clarified liquid, an associated clarifying process may remove suspended solid particles leaving a substantially further clarified fluid.
One type of fluid separation technique may include a membrane filtration process. Typically, a membrane filtration process removes particles from a liquid by retaining the particles in a filter of a specific size suited for a particular application. Some examples of membrane filtration processes include microfiltration, ultrafiltration, and nanofiltration. For insoluble particles, microfiltration can be used to retain and remove these particles from a liquid. Ultrafiltration may define a purification process that serves as a primary purification filter to isolate a desired solid product of a specific size. A nanofiltration process may be used in a final purification process to remove contaminants as small as microscopic bacterial cyst.
Another example of a fluid separation technique may include centrifugal separation. In centrifugal separation, a centrifuge may use centrifugal force to separate more dense contaminants from a fluid medium to leave a clarified fluid. By creating a centrifugal force several times greater than gravity, more dense contaminants separate from the fluid medium. To create centrifugal force within the centrifuge, the fluid medium is often placed within a chamber that rotates along a symmetrical axis creating the centrifugal force in a radial direction away from the symmetrical axis. More dense contaminants suspended in the fluid medium are forced against an outer wall of the rotating chamber and may pass through openings in the chamber to an outer catchment basin. The resulting clarified fluid, which is less dense, remains near the axis of rotation and may typically be removed from the chamber via a clarified fluid outlet.
As more dense contaminants are extracted from the fluid medium, the openings formed in the wall that allow the more dense contaminants to be expelled from the rotating chamber may become clogged with particulate matter or solids. Despite high centrifugal force, particulate matter may clog the openings and create a build up of relatively solid materials behind this “clog-point”. Once an opening is clogged, the centrifuge must be stopped and the clog cleared in order for the centrifuge to be returned to service.
Another problem may exist within the centrifuge due to the rotation of the chamber. As the chamber rotates around a center axis, inertia or momentum of the fluid medium being rotated may develop an inner swirling pattern within the chamber, known as a cyclonic vorticity. Because this vorticity often creates an agitation within the associated chambers, it may be desired to avoid this cyclonic vorticity effect by limiting rotational speeds.
One method of controlling a centrifugal separation process is to control the release of the more dense contaminants from the rotating chamber. To control this release, the opening in the chamber may be used to vary the amount of more dense contaminants moving through the passage. Some of the problems associated controlling the release of more dense contaminants through the opening include the direction of valve movement, the location of the valve members, and the location of the actuator for controlling the valve.